Pembrolizumab and Doxorubicin Hydrochloride or Anti-Estrogen Therapy in Treating Patients With Triple-Negative or Hormone Receptor-Positive Metastatic Breast Cancer

This phase II trial studies how well pembrolizumab and doxorubicin hydrochloride works compared to pembrolizumab with anti-estrogen therapy (anastrozole, letrozole, or exemestane) in treating patients with triple-negative or hormone-receptor positive breast cancer that has spread from the primary site (place where it started) to other places in the body. Pembrolizumab is an antibody drug that blocks a molecule called programmed death (PD)-1. PD-1 is a molecule that shuts down the body's immune responses and prevents the immune system from attacking the cancer. Doxorubicin hydrochloride is a drug used in chemotherapy that works to stop the growth of tumor cells by stopping them from dividing and by causing them to die. Anti-estrogen therapy, including anastrozole, letrozole, and exemestane, lowers estrogen levels in the body, which may help treat cancer that is hormone receptor-positive. Giving pembrolizumab together with standard treatment of either doxorubicin hydrochloride (triple-negative cancer) or anti-estrogen therapy (hormone receptor-positive cancer) may be an effective treatment for these types of breast cancer.